Recently, increasing attention has been given to the development of dynamic route guidance systems and integrated and adaptive traffic control strategies.
Dynamic traffic assignment (DTA) has been one of the most recent developments receiving extensive attention in the transportation research communities worldwide [DYNA(1992-1995), FHWA(1995), Mahmassani et al.(1994), MIT(1996)]. DTA aims at providing route guidance based on predicted rather than historically measured traffic conditions. While various DTA systems are still undergoing theoretical research as the state of the art, a variety of route guidance systems are being subjected to experiment in real-world traffic networks. For example, dynamic route information panel (DRIP) is being used to provide short-term traffic forecasts for several major urban arterials in Amsterdam, the Netherlands [von Toorenburg et al.(1996)]. ADVANCE, an real-time in-vehicle route guidance system, is under field test in a suburban area in Chicago, Illinois.
Frameworks for hierarchical or multi-level traffic control have been suggested by several researchers including [Head et al.(1992)]; and [Gartner et al.(1995)]. [Gartner et al.(1995)] reviewed the past experiences with ``advanced'' traffic signal control strategies and suggested a multi-level design of real-time, adaptive signal control strategies. They emphasized that a system should offer varying degrees of responsiveness, depending on particular network and traffic characteristics. In addition, the system should allow selection of a control strategy when such a strategy could provide the greatest benefits and maximize the overall effectiveness of the particular system. To meet these requirements, a real-time traffic adaptive control system (RT-TRACS) is under development [Tarnoff and Gartner(1993)]. Frameworks for integrating dynamic traffic assignment with real-time traffic adaptive control have been proposed [Gartner and Stamatiadis(1997), Chen and Hsueh(1997)]. A decentralized scheme for real-time route guidance was also proposed [Hawas and Mahmassani(1995)].
The EUROCOR project [Middelham et al.(1994a)] is another recent example of development and application of a sophisticated traffic control system. EUROCOR, with special attention to ramp metering, is part of the European multi-national DRIVE-2 project, which includes the development and evaluation of integrated urban corridor control models. EUROCOR's main objectives were to develop and apply dynamic traffic control models for effective management of traffic in freeway corridors using traffic signals, ramp metering, and variable message signs (VMS). The system has undergone extensive field trials on a limited set of corridors around certain cities [Diakaki and Papageorgiou(1995), Middelham et al.(1994a)].